The present invention relates to seals between rotating and stationary components of a rotary machine such as a steam turbine and particularly relates to apparatus and methods for supporting variable clearance packing ring segments to prevent circumferential slippage of the segments about the grooves of the stationary component, while enabling the segments to move toward and away from the rotating component, i.e., between large and small clearance positions relative to the rotating component.
In prior U.S. Pat. No. 5,709,388, of common assignee herewith, there is disclosed a rotary machine such as a steam turbine having upper and lower housings secured to one another about a horizontal midline. Each housing includes an arcuate groove having a dovetail shape, i.e., has locating flanges directed axially toward one another and defining a slot therebetween for receiving a plurality of annular segments. Each of the annular segments includes an arcuate seal face for opposition to the sealing surface of the rotating component and which seal face typically carries radially directed axially spaced labyrinth seal teeth. Each seal ring segment also has a similar dovetail shape including a pair of flanges directed axially away from one another for disposition within the dovetail groove of the stationary component and a neck which joins the seal face and the flanges of the segment and passes through the slot defined by the locating flanges of the groove.
As disclosed in the aforementioned patent, three segments are disposed in the upper half and three in the lower half of the housing. The side segments in the lower housing are supported against downward circumferential displacement in the groove of the lower housing by angle brackets. It is necessary to support the side segments to prevent binding of the lowermost segment in the lower housing with the side segments to prevent radial inward (upward) displacement of the lowermost segment under steam pressure as necessary to effect the seal. One leg of each angle bracket is secured to the outer uppermost side of a side segment in the lower housing and the opposite leg is supported on a surface of a slot machined into the lower housing, the slot opening through the horizontal midline. The horizontal leg of each bracket supports the associated side segment for horizontal movement toward and away from the rotating component. It will be appreciated that the variable clearance packing ring segments are spring-biased into outward clearance positions relative to the rotor shaft and, in operation, are biased by fluid pressure into smaller inner clearance positions relative to the shaft to effect the operating seal.
Standard non-retractable packing rings require a machined slot within the upper housing at the diaphragm horizontal joint. To update rotary machines using non-retractable packing rings to machines having retractable packing rings, the lower housing, according to the aforementioned patent, requires the formation of a notch or slot adjacent the horizontal midline, together with the provision of steam feed holes to be drilled into both housing halves. This has significant impact on the installation cycle requiring substantial time to effect the changeover. As will be appreciated, any modification to the diaphragm halves, particularly the lower housing half, to accommodate the variable clearance packing ring segments, by forming a slot or notch, increases the power plant outage cycle time at substantial expense to the electrical utility employing the steam turbine. Accordingly, there is a need to reduce the cycle time when retrofitting a steam turbine with variable clearance packing ring segments.
In accordance with a preferred embodiment of the present invention, there is provided apparatus and methods for supporting upper and lower packing ring segments in the upper and lower housings, respectively. Preferably, packing ring segments are retrofitted in machines using non-retractable packing rings without requiring modification of the lower housing in order to accommodate the segment support brackets, thereby reducing installation cycle time. Particularly, instead of supporting the outwardly projecting horizontal legs of the angle brackets supporting the side segments in the lower housing in notches or slots of the diaphragm, those segments are supported by portions of the surface of the lower housing at the horizontal midline. Accordingly, the formation of a slot or notch along opposite sides of the lower housing at the horizontal midline is unnecessary. The upper housing has an existing slot opening through the horizontal midline in which is received a stop for supporting the side segments in the upper housing. Each horizontal outwardly projecting leg of the support member for a side segment of the lower housing is also disposed in the same slot. It will be appreciated that the slot in the upper housing is preexisting and requires no further machining or other reworking to accommodate both the stop and the bracket portion. The brackets, and hence the side segments in the lower housing are thus slidable horizontally on a surface portion of the horizontal midline of the lower housing between the small and large clearance positions.
In a preferred embodiment according to the present invention, there is provided a rotary machine comprising a component rotatable about an axis, a stationary component including upper and lower housings of the machine joined together along a horizontal midline and an annular groove about the axis, the lower housing including a support surface along and coincident with the horizontal midline, the stationary component having a first axially directed locating flange about the axis and in part defining a slot opening into the groove, a plurality of generally arcuate seal ring segments about the axis, each segment having an arcuate sealing face, a second axially directed locating flange disposed in the groove and a neck portion in the slot and interconnecting the second flange and the sealing face, certain of the plurality of the segments being movable between radial outward and radial inward positions relative to the axis, a member engaging between the support surface along the horizontal midline of the stationary component and each of a pair of the plurality of segments on respective opposite sides of the lower housing of the stationary component for supporting the pair of segments for movement generally horizontally toward and away from a vertical plane through the axis between inner and outer positions, respectively, and fixing the pair of segments against vertical downward movement, the pair of segments comprising different ones of the plurality of segments than the certain segments, the pair of segments being disposed in the lower housing of the stationary component and straddling another segment of the plurality of the segments in the lower housing whereby each member maintains a gap between the lower end of one of the pair of segments and an opposing end of another segment when the certain segments lie in radially outward positions and the pair of segments lie in the outer positions.
In a further preferred embodiment according to the present invention, there is provided a rotary machine comprising a component rotatable about an axis, a stationary component including an annular groove about the axis, the stationary component comprising upper and lower housings joined to one another along a generally horizontal midline of the stationary component, the upper housing including a radially inwardly opening slot on opposite sides of the stationary component defined in part by an upper surface portion of the lower housing forming part of the horizontal midline, the stationary component having a first pair of axially directed locating flanges about the axis and extending axially toward one another, the flanges defining a slot opening into the groove, a plurality of generally annular segments about the axis, each segment having an arcuate sealing face, a second pair of locating flanges disposed in the groove and extending axially away from one another and a neck portion in the slot and interconnecting the second flanges and the seal faces, at least three of the plurality of segments being disposed in each of the upper and lower housings and forming a circumferentially extending seal ring about the rotatable component, the segments being movable between outward large and inward small clearance positions relative to the rotatable component and members engaging between the lower housing along the upper surface portions thereof and a pair of the segments on respective opposite sides of the lower housing for supporting the pair of segments against displacement in the groove in a circumferentially downward direction and for movement generally horizontally toward and away from a vertical plane through the axis and between inward and outward positions, respectively.
In a further preferred embodiment according to the present invention, there is provided in a rotary machine having a component rotatable about an axis, a stationary component including upper and lower housings joined together at a horizontal midline and an annular groove about the axis, a plurality of generally annular segments about the axis with at least a portion of each segment disposed in the groove and having a seal face projecting from the groove, a method of installing the segments into the rotary machine, comprising the steps of securing a support member to each of a pair of the plurality of segments on respective opposite sides of the lower housing of the stationary component and locating a horizontally projecting outward portion of the member along a surface of the lower housing forming part of the horizontal midline between the upper and lower housings for supporting the pair of segments for movement generally horizontally toward and away from a vertical plane through the axis between inner and outer positions, respectively, and fixing the pair of segments against vertical downward movement.